In Allen County’s otherwise gently rolling moraines and flat outwash plains, sluiceways
and lake beds, the Cedar Creek valley’s topography is unique.
As Cedar Creek makes an abrupt turn eastward at Coldwater Road, it flows through one
of Indiana’s most dramatic examples of a glacial tunnel valley. This valley extends
east for about 5 miles from the tunnel’s mouth at Coldwater Road. The valley canyon
averages about 1000 feet wide, and in some places, as much as 80 feet deep.
The tunnel valley formed when glacial meltwater, flowing under pressure, eroded a
channel into the earth beneath the ice. When the ice disappeared, a deep ravine or
canyon remained as evidence of the extensive excavation that had taken place—the
In geological terms, the Cedar Creek valley is young, formed when the Erie lobe of the
Wisconsin Glacier receded about 15,000 to 20,000 years ago. The valley was cut into
deposits that formed the Wabash Moraine (an accumulation of soil and rocks distributed
by the glacier). This rock and soil sediment washed westward from the valley into the
adjacent Eel River sluiceway.
Subsequent erosion on the valley’s floor led to a “beheading” or capture of the Cedar
Creek that reversed the stream’s original westward flow through the tunnel valley to
its present eastward direction.